M.A. Thesis:

The effect of tragacanth gum٫ lecithin and plum humectant on the physicochemical٫ rheological and sensory evaluation of flat bread staling process

Bread is the most important food products and one of the main parts of the Iranian families food basket. The main aim of this study was to evaluate different concentrations humectant (three levels 0, 3 and 6%), tragacanth (at three levels 0, 0.75 and 1.5 percent), lecithin as a emulsifier in three levels (0, 0.5 and 1%) In combination with the formulation of flat bread (barbarian). To prepare bread formulations, routine industrial formulation and process was used. Dough samples were prepared in 300 gram pieces, then passed the initial, medial, and final fermentation stage baking machines were imported. After cooling samples , they were studied by water activity (aw), moisture, color analysis, total acceptance and specific volume and rheological properties.To evaluate the effect of adding different additives mentioned on bread staling, after two days, the cooked and stored at ambient temperature samples were investigated for the rheological properties such as elasticity and firmness. These experiments performed in response surface methodology and due to the number of treatments done twice. The results showed a significant correlation (P <0.01) in reducing rheological properties of bread using lecithin and tragacanth. humectant although increased elasticity and strength that is required for tearing bread but at 6% concentration of humectant the amount of force and elasticity were held for 2 days decreased. The amount of water activity by only increasing tragacanth significantly (P <0.01) decreased. Moisture content and specific volume of bread by adding all independent variables a significantly effected (P <0.01) is. The total acceptance of bread only by the humectant concentration and this index has increased over usual average concentrations and bread colors became very bright. Lecithin is the most important factor affecting the indexes a * b * color leaning to bread samples became red. Tragacanth reduce the index b * of samples, thus reducing the intensity of the yellow color and humectant and lecithin caused increasing this factor and thus create more yellow color in bread.

Keywords: Keywords: flat bread, rheological properties, plum hmectant , tragacanth, lecithin